The geologic record places the modern sea-level rise into an historical context and can help inform discussions of the rates and magnitudes of future sea-level rise. With the development of large Northern Hemisphere ice sheets at 2.7 Ma, amplitudes of sea-level change increased, reaching over 100 m at times. A globally average sea-level rise of ~130 m followed the last ice age. We construct 21st century relative sea-level rise scenarios including global, regional, and local processes and project a 22 cm rise at bedrock locations by 2030.
The geologic record places the modern sea-level rise into an historical context and can help inform discussions of the rates and magnitudes of future sea-level rise. During the Pliocene, CO2 levels were similar to 2014 (400 ppm), yet temperatures were globally 2°C warmer and global average sea level stood globally 22±10 m above present.
With the development of large Northern Hemisphere ice sheets at 2.7 Ma, amplitudes of sea-level change increased, reaching over 100 m at times. A globally average sea-level rise of ~130 m followed the last ice age, with rates that at times exceeded by ten times the modern rate of rise (> 40 mm/yr versus ~ 3 mm/yr). Rates of rise along the U.S. Gulf and much of the U.S. Atlantic coasts were higher due to Glacial Isostatic Adjustment and local subsidence.
The rate of relative sea-level rise in the U.S. mid-Atlantic region decreased from 3.5±1.0 m/yr at 7.5-6.5 ka, to 2.2±0.8 mm/y at 5.5-4.5 ka, to a minimum of 0.9±0.4 mm/yr at 3.3-2.3 ka. Relative sea level rose at a rate of 1.6±0.1 mm/yr from 2.2 ka to 1.2 ka (750 CE) and 1.4±0.1 mm/yr from 800-1800 CE. Geological and tide-gauge data show that sea-level rise was more rapid throughout the region since the Industrial Revolution (19th century = 2.7±0.4 mm/yr; 20th century = 3.8±0.2 mm/yr).
There is a 95% probability the 20th century rate of sea-level rise was faster than it was in any century in the last 4.3 kyr. These records reflect global rise (~1.7±0.2 mm/yr since 1880 CE) and subsidence from glacio-isostatic adjustment (~1.3±0.4 mm/yr) at bedrock locations (e.g., New York City, Philadelphia, Baltimore, and Washington D.C.). At coastal plain locations, the rate of rise is 0.3-1.3 mm/yr higher due to groundwater withdrawal and compaction.
We construct 21st century relative sea-level rise scenarios including global, regional, and local processes. We project a 22 cm rise at bedrock locations by 2030 (central scenario; low- and high-end scenarios with a range of 16-38 cm), 40 cm by 2050 (range 28-65 cm), and 96 cm by 2100 (range 66-168 cm), with coastal plain locations having higher rises (3, 5-6, and 10-12 cm higher, respectively). By 2050 CE in the central scenario, a storm with a 10-year recurrence interval will exceed all historic storms at coastal locations.